That was very, very well done. The gameplay is really solid, the art looks good, and the music fits well. I think in this case the whole really is more than the sum of its parts; everything works together really well.
I found it really difficult the first time around, but the second time I had less trouble. I think it helped that I was using a controller, and wasn't dealing with the performance issues (I turned effects off). Still, I wish there were more save points.
I thought the boss was too easy at first, and then it changed up its attacks which threw me off balance. I was still able to beat it on the first try, though.
I also wasn't able to execute some of the attacks. I'm not sure if this was a bug or if I was just doing it wrong. I was able to do fine with the ones I could pull off, though.
I'm not familiar with Madoka Magica or Bloodborne so I'll take your word for it.